If a malfunction occurs in a mobile network the standard procedure is that the responsible network element reports it to the Operations Support System (OSS) of the mobile network in the form of an alarm. The network element also indicates the cause of the malfunction, if this is available. There are, however, malfunctions that have no explicit sign or cause. These cases may be relatively easy to observe and identify but the detection of the error or malfunction requires advanced techniques and preliminary analysis of the network events prior to or during the occurrence of the error or malfunction.
A common example of such a malfunction which can occur in a mobile network is called “sleeping cell”. A sleeping cell is a cell which is not functioning properly, in the sense that it cannot properly serve the mobile devices which are in its coverage area. The malfunction can have an impact on the whole cell functionality, i.e. no mobile device can contact the network through the given cell. It may also be a partial functionality malfunction e.g. a mobile device may be able to use the signalling channels but not be able to send/receive IP data packets. Since the symptoms of a sleeping cell can be very diverse and mostly only visible through the traffic statistics, there is no single detection mechanism that can provide a fully reliable validation about the health of a cell.
There are different solutions existing on how to validate if a cell is a sleeping cell. US Patent Application US20100234006 describes the use of the number of RRC Requests and the success rate as an indicator for a sleeping cell.
US Patent Application US20110037601 describes a distributed detection algorithm where the sleeping cell validation is supported by alarms received from the neighbour cells.
EP1638253 and CN101594622 describe statistical approaches where cell performance is compared to a predefined threshold or historical performance to detect any abnormal behaviour.
CN102281555 proposes a solution for the validation of the erroneous state of a cell by sending a special type of “broadcast” paging message in the cell and observe if any mobile device is responding to this broadcast paging message. The “broadcast paging” also includes a detection indication information and pages all mobile devices in a given cell. In practical realization this requires extensive standardization effort, since the current 3GPP standards do not support this kind of “detection indication”. Furthermore, the cell broadcast paging is not usable for forcing a mobile device to send any signal to the base station but only to update its system information by re-reading the cell broadcast channel.
CN102388644 describes the usage of a dedicated function in the base station to simulate a “test user” to see if the cell behaves normally. The main drawback of this solution is that a simulation cannot cover all potential errors. In fact, since the errors are far from being trivial (otherwise there would be an alarm for it), it is very likely that the problem remains hidden. Moreover, the error can be outside the simulation scope, e.g. some hardware, antenna problem.
All the solutions described above also require as much verification as possible to avoid false alarms. This makes their execution cumbersome and still the validation of a sleeping cell is not guaranteed.